Made of stone or metal, and often larger than life, monuments are meant to be permanent. The most celebrated ones are public memorials, built by governments and placed in communal spaces such as parks or in front of courthouses, presidential mansions, or other official buildings. Indeed the most massive, elaborate, or decorative government buildings act as monuments themselves.

This should not mean, however, that monuments are held as eternally sacred symbols. They reflect the particular historical circumstances of their creation, and their meanings can change over time.

In the U.S., this theme has come to the forefront following the recent violence sparked by white supremacists, fascists and neo-Nazis who rallied against the removal of a particular statue. The statue is one of dozens around the country commemorating Robert E. Lee, the military commander of the Confederate States of America, the name for those territories that seceded from the United States to start the American Civil War in 1861.

Although a shocking number of Americans still refuse to acknowledge it, the civil war was undeniably fought over slavery. Those who insist that the war was actually fought over "states' rights" and the southern way of life seem to miss the point that what the Confederacy defended was the states' rights to keep slavery, which formed the basis of the South's way of life.

Therefore, today's indignant protectors of such statues are upholding none other than the heritage of white supremacy, racial segregation and forced labor, which cannot be separated from anything else that distinguished the southern lifestyle. The Confederate leaders themselves said so, explicitly, when they rebelled back in the 1860s.

Today's defenders of Confederate symbols also seem unable to recognize that as time passes, societies and worldviews change with new information and understanding. Just as we no longer can accept slavery and racial discrimination, it is difficult to accept public memorials to ideas and people behind the violence of slave labor, ethnic cleansing, and systematic rape. (If we are stuck, we can always apply the Hitler test: Could anyone justify keeping an old statue of the Nazi leader for the sake of historical preservation?)

So look for further battles to come, as concerned Americans challenge more monuments and statues, not only of those southern leaders who promoted slavery and discrimination, but even of older, iconic figures like Christopher Columbus, the Spanish seafarer whose voyage in 1492 changed the world. Over the past few centuries, so central did Columbus become to the mythology of the Americas that his name became attached to just about everything: companies and institutions, schools and universities, a broadcasting network (CBS) and of course innumerable places. Indeed the US capital is ultimately named after him, as is an entire country in South America.

But historians have discovered something in documents such as eyewitness accounts, as well as his own diaries and reports: Columbus was not only a daring, if somewhat delusional, explorer, but also a murderous maniac, blithely killing or enslaving native Americans in pursuit of riches and in the name of his religion and monarch. And of course his actions began the waves of genocide that killed countless millions of indigenous people from the 16th to 19th centuries, mostly through disease but also through targeted violence. Together with the transatlantic slave trade, another practice that Columbus initiated, this extermination of the western hemisphere's inhabitants made possible the European domination of the Americas.

One can accept this as simply the deeply disturbing reality of the past from which we can learn, and at least it's an improvement over the myths that were common until recently. But should we also simply accept the continuing display of statues, in public spaces, of people like Columbus? After all, these monuments honor not only a troubling historical figure but also past eras when such a man was ignorantly glorified.

Like many other nationalities in the modern world, South Koreans have become familiar with the sensitivities of such a problem. But they have mostly recognized that monuments, like laws and governments, are living things, originating in the past but continually refreshed with meaning as times and values change and knowledge is gained.

Back in 1995, for example, some observers, including historians, opposed President Kim Young Sam's decision to take down the enormous building behind Seoul's Gwanghwamun Gate that had been erected, seventy years earlier, as the headquarters of the Japanese colonial government. Those who objected to Kim's decision argued that the building was distinctive, historically valuable, and reflected an undeniably important period in Korea's past, however unsettling.

But this building was also constructed to serve as a monument to Japanese rule and all that came with it. Hence, despite its utility as a spacious structure that South Korean governments had used for fifty years after liberation in 1945, its continued existence in such a prominent public space could no longer be endured in a new, democratic South Korea. In short, times had changed.

Removing outdated and inappropriate public memorials, in other words, is just as historically valid as keeping them in place. If they cannot be transferred to museums, then destruction seems unavoidable.

This point might prove useful when the current North Korean regime falls, and all those huge monuments to the Kims and to "Juche" will likely be torn down. We don't know when this will happen, but it's difficult to imagine that Koreans liberated from totalitarian rule will accept calls to save these monuments in the name of historical preservation.

Kyung Moon Hwang is a professor at the Department of History, University of Southern California. He is the author of "A History of Korea-An Episodic Narrative" (Second edition, Palgrave Macmillan, 2016). Contact khwang3@gmail.com.